Project summary Social anxiety disorder (or social phobia) is the most common form of anxiety disorder in the United States. Affected individuals avoid social contexts, which disrupts social relationships and impairs performance at school or work. New therapeutic approaches are needed because ~40% of affected individuals who seek existing treatments do not respond. Oxytocin is a well-known modulator of social behaviors, and has been put forth as a possible therapeutic. In some studies using human participants, intranasal oxytocin enhances social approach related behaviors. However, other studies (especially in women) report that intranasal oxytocin increases social anxiety. How can the same neuropeptide exert such different effects on behavior? Our central hypothesis is that oxytocin acts in the mesolimbic dopamine system to promote social approach, whereas oxytocin acts in the bed nucleus of the stria terminalis (BNST) to enhance social anxiety. This hypothesis is conceptually innovative because it can reconcile apparently contradictory findings in both human and animal studies of oxytocin function. The proposed studies will test this hypothesis in both males and females because social anxiety disorder is more prevalent in women than men. Our studies will use the California mouse social defeat model, which induces a stronger social anxiety phenotype in females versus males. First, we will use antisense morpholinos to selectively inhibit oxytocin synthesis in neurons within the BNST or hypothalamus (which project to the nucleus accumbens, NAc) to determine how these cells modulate social anxiety and social approach. Next, we will use viral vectors to visualize oxytocin producing cells in the BNST and hypothalamus. We will isolate oxytocin neurons for single-cell RNAseq analyses, and we will also conduct electrophysiological analyses. We will determine the extent to which social stress induces molecular and physiological responses that increase excitability. Finally, we will study the behavioral effects of oxytocin receptor (OTR) in the NAc and BNST using biased agonists that selectively induce OTR coupling of either Gq or Gi pathways. Our research team is ideally suited to execute these studies. Dr. Trainor's lab developed the California mouse social defeat model and collected most of the preliminary data. Dr. Robison is a behavioral neuroscientist with strong molecular and electrophysiology skills. Dr. Settles is an expert in bioinformatics and performed analyses of single-cell RNAseq data. Dr. Chini is a leading authority on OTR G-protein coupling and provides expertise for pharmacology studies. Dr. Grinevich developed viral tools for targeting oxytocin neurons and provides viruses and advice. Our analyses of how stress alters the physiological and molecular phenotypes of distinct populations of oxytocin neurons from males and females are unprecedented, and could lead to novel insights into how to selectively target these cells.